Size controlled mechanochemical synthesis of ZrSi2.

Mechanochemical metathesis reactions were utilized to synthesize nanocrystalline ZrSi(2) ranging from 9-30 nm in size. Size was controlled through dilution with CaCl(2). A linear relationship was found between diluent concentration and crystallite size. Unlike typical self-propagating metathesis reactions, this reaction did not self-propagate, requiring the input of mechanical energy.

Synthesis and crystal structure of cubic Ca16Si17N34.

Since the late 1960s, the exact structure of cubic calcium silicon nitride has been a source of debate. This paper offers evidence that the cubic phase CaSiN(2) described in the literature is actually Ca(16)Si(17)N(34). Presented here is a method for synthesizing single crystals of cubic-calcium silicon nitride from calcium nitride and elemental silicon under flowing nitrogen at 1500 °C. The colorless millimeter-sized crystals of Ca(16)Si(17)N(34) with a refractive index (n(25)) = 1.590 were found to be cubic (a = 14.8882 Å) and belong to the space group F43m (216). The synthesis of bulk, powdered cubic-Ca(16)Si(17)N(34) from calcium cyanamide and silicon is also discussed. Ca(16)Si(17)N(34) is a relatively air-stable refractory ceramic. In contrast to the orthorhombic phase of CaSiN(2), in which Ca(2+) sits in octahedral sites, this cubic phase has Ca(2+) in cubic sites that makes it an interesting host for new phosphors and gives rise to unique crystal field splitting.

Mechanochemical synthesis of alkaline Earth carbides and intercalation compounds.

High-energy ball milling has been successfully employed to produce alkaline earth carbides from the elements. In particular, CaC(2) yields of up to 98% can be realized in as little as 12 h. Similarly, the carbides of Mg (39% yield), Sr (87% yield), and Ba (82% yield) have been prepared. An intermediate in the synthesis of CaC(2) is the newly discovered gold-colored Ca-graphite intercalation compound CaC(6). Sr and Ba also go through initial intercalation phases (SrC(6) and BaC(6)) before ultimately producing the carbides. The magnesium product consisted of Mg(2)C(3) with no MgC(2) observed. The addition of sulfur to CaC(2) forming reactions did not adversely affect the overall synthesis; this suggests that this method may be utilized to sequester sulfur from high-sulfur coal. The preparation of these compounds by high-energy ball milling represents a novel method for producing pure carbides, as well as a convenient route to isotopically enriched ethyne.